From Sahih Muslim (Hadith 2193):
Abu Huraira reported Allah's Messenger (ﷺ) as saying:He who offers prayer for the dead, for him is (the reward of) one qirat; and he who follows the bier till it is placed in the grave, for him (is the reward of) two qirats. I (Abu Hazim, one of the narrators) said: Abu Huraira, what is a qirat? He said: It is like the hill of Uhud
Reference: Muslim 2193